On a crop sensor I have used the 50mm compact macro, 60mm, 100mm (non-L), and 180mm. The 180mm is by far the best macro lens I have ever used (I have not used the 100mm L). As neuro says, it's basically how much working distance you want and how much money you are willing to spend. They are all fantastic lenses. If I had to rate them from sharpest to softest, my list would like like this: 180mm > 100mm > 50mm > 60mm. In terms of build quality, just flip the 50mm and 60mm position. As someone else mentioned, if you are budget conscience, the 50mm f1.4 also works well with the 12mm extension tube (at least as sharp as the 60mm macro) and provides decent macro with the added benefit of a good low light lens for other uses.